A Cargo Container is one of many objects found scattered around Timberwolf Mountain in The Long Dark. They can typically be found by bits of broken plane wreckage scattered around the map. Most can be found in the Tail Section at the summit.
They usually have two distinct items in large quantities, totally up to a dozen or more separate pieces. Possible items include:
Notably, this is the only way to get pelts from a source other than a dead animal.
It also takes a minute or two to hack off the lock with the hacksaw. Make sure you are secure from wildlife, as many of the crates are close to predators.
Be aware that there are two sections to each individual crate. Both sections are separately locked and have separate items.